Gear shaving hob



Filed Oct. 6, 1942 /a /0 in g- M W a T .m m fim Q2 r 4 HM z M Patented May 16, 1944 GEAR SHAVING HOB Harry Pelphrey, Detroit, Mich, assignor to Michigan Tool Company, Detroit, Mich a corporation of Delaware Application October 6, 1942, Serial No. 460,975

3 Claims.

The present invention relates to a gear shaving hob and particularly relates to a globoidal cutting tool for shaving a worm gear of the I-Iindley typ One of the primary objects of the present invention is to provide a novel shaving hobof the type mentioned by which the teeth of a worm gear of the Hindley type may be accurately finished.

Another object of the invention is to provide a novel shaving hob, of the type mentioned, in which the cutting or shaving edges are provided on a portion of the hob only with the remaining portion being smooth so that such remaining portion engages the teeth of the gear being finished and serves to insure proper intermeshingrelationship between the hob and the gear being finished in a simplified manner.

Other objects of the invention will become apparent from the following specification, the drawing relating thereto and from the claims hereinafter set forth.

In the drawing in which like numerals are used to designate like parts in the several views throughout;

Figure 1 is a cross sectional view, with parts in elevation, of a shaving hob embodying features of the present invention and illustrating such hob in intermeshing relationship with a Hindley type gear being finished;

Fig. 2 is a cross sectional view taken substantially along the line 2-2 of Fig. l

Fig. 3 is a perspective view of that portion of the hobupon which the cutting edges are formed: and

Fig. 4 is an enlarged sectional view taken substantially along the line 4-4 01' Fig. 3 and illustrating the form of the cutting edges.

In order that'a complete understanding of the present invention may be had, reference should be given to the particular type of worm gear to which the present invention relates. For underwhich are tangent to a circle, whose center c0- incides with the axis of the wheel with which the worm is adapted to mesh.

It has been found that in gearing of this type the axial length of the work portions of the sides of the thread of the worm cannot extend throughout a greater over-all axial distance than the diameter of the circle above mentioned to which the thread sides are tangent, and which may be termed the base circle of the worm. The radius of this base circle is determined by the pressure angle of the teeth of the worm.

It will be appreciated that in the formation of the thread or threads of the worm, the sides of the thread are determined by tangents to this base circle. Therefore, from one end of the worm, one of the sides adjacent that one end will be substantially at a right angle to the axis of the worm. The opposite, side of the thread at the same end of the worm, is tangent to the opposite A side of the base circle and such opposite side of standing of such generalytype of gear, reference may be had to Cone ,Patents Nos. 1,885,686 and In the Cone type of double enveloping worm gearing, the sides of the thread of the worm have sinuously warped surfaces, which surfaces are generated by a straight line element. straight line element lies in a plane passing through the axis of the worm and perpendicular to the axis of the wheel with which the worm is adapted to mesh. The intersections of the tooth sides-.with this plane all lie along straight lines This the thread will be at an angle to the axis of the worm. The first mentioned side of the thread which is at substantially a right angle to the axis of the worm is termed the right angle side 01 the thread, while the opposite side is termed the angular side of the thread. As the right angle side of the thread approaches the central portion of the worm, that side becomes more angular so that as it passes over the central portion of the worm it becomes the angular side of the thread, in that such sides are formed as tangents to the opposite side of the base cir 1e. Also, the angular side of thread, taken from he first mentioned end of the wormfi'becomes a smaller angle as it approaches the central portion of the worm and as it passes beyond the central portion of the worm, the same side becomes the right angle side of the thread.

According to the present invention the cutting edges are provided on the right angle portion of one of the sides of the thread only. The remaining angular portion of the same side' of the thread and the angular and right angular portions of the opposite side oi the thread are smooth. The sinuously warped thread on the hob of the present invention is generally of the same form as the globoidal type of worm above referred to.

More specifically, the hob of the present invention is constructed in a pair of sections which Justed position with respect to each other. The cutting edges are formed on the right angle side of the thread on one of the sections only. The hob is then mounted in meshing relation, on proper center distances, with respect to the gear to be finished. The hob sections are circumferentially adjusted with respect to each other so that the cutting edges on the right angle side of one of the sections will engage one side of the teeth to be finished, while the opposite side of the teeth is engaged by the right angle side of the thread on the other section. The right angle side of the thread on the second tooth section, as mentioned above, is smooth. This insures a proper intermeshing relationship between the shaving hob and the gear to be cut so that it is merely necessary to run the hob in mesh with the gear to be out without the need of relatively complicated gearing interconnecting theworm spindle and the gear spindle.

Referring to the drawing, the gear shaving hob is generalhr indicated at l8, and is generally of the form of the globoidal type of worm mentioned above. Such hob is shown in its meshing relationship with a worm gear I! of the Hindley or enveloping type. The hob I8 is formed of a pair of sections I4 and It. A portion of the worm thread l8'is formed on the section l4, while the remaining portion 20 of the worm thread is formed on the section It. A single thread is illustrated, but it will be appreciated that a plurality of threads may be employed within the scope of the present invention.

The thread portion I8 is formed integrally with, and machined on a shaft 22 having a reduced end portion 24 which is supported by suitable bearings 26 which are retained on the shaft portion by a nut 28. Another shaft portion 30 is formed integrally with the section I4 and extends from the opposite end of the threaded section l4 in axial alignment with the shaft 22. Such shaft portion 30 serves to support the other section l8 of the hob which is in the form of a sleeve or collar, having the remaining portion of the thread 28 formed thereon. The remaining portion of the thread, of course, is a continuation of the thread l8.

The collar section l8 has a pair of conventional worm elements 32 mounted within recesses 84 formed therein, which mesh with a plurality of teeth 86 cut into the shaft portion 30. The worm, elements 82 are employed to revolve the collar section 18 relative to the shaft portion 30 to retain the sleeve in adjusted position. The means for adjusting the two sections l4 and IS with respect to each other is the same as that employed in the adjustable worm described in Pelphrey Patent No. 2,165,761, issued July 11, 1939, and reference may be had to such patent for detailed description of the locking or binding action.

A bearing 38 is mounted on the shaft portion 80 and is retained thereon by means of a nut 40. The bearings 28 and 38 are disposed in axial alignment and are mounted upon suitable standards 42 which are disposed for mounting the shaving hob ID a proper center distance and with the plane of the axis of the hob It in the proper relationship with respect to the worm gear l2. The shaft portion 30 may extend beyond the standard and be connected to suitable drive means.

Considering section M of the hob, the thread l8 has a right angle side 44 and an angular side 48. The right angle side 44 becomes the angular side of the thread on section It and the angular side 48 becomes the right angle side of the thread portion 20 on section l8. This is due to the tangential relationship of the sides of the thread to the base circle as discussed above. The angular side 46 of section I4 and both the right angle and angular sides of the thread 28 on section I8, remain smooth. The shaving or cutting edges are formed on the right angle side 44 of section l4 only. The shape and arrangement of such cutting edges are best illustrated in Figs. 3 and 4, and it will there be seen that the cutting edges are formed in the right angle face 44 and extend at an angle to the radial from the root to the crest of the thread. The cutting edges are formed by a plurality of spaced grooves 48 formed in the right angle face at an angle to the radial from the root to the crest of the thread. The grooves 48 have side walls 50 for interconnection with the face 44 at substantially right angles thereto and provide cutting edges 52 those portion of the face between the cutting edges form lands and all of such lands lie in a common smooth surface. The grooves 48 are of materially less depth than the thickness of the threads. The lands are of such width that a shaving of the teeth of the worm gear may be accomplished without undue pressure.

The grooves 48, which form the cutting edges may be formed by a machining operation but this is difdcult to do since the width of the grooves varies from the root to the crest of the thread, the width of the lands being constant. It is, therefore, preferable that the grooves be formed by an etching process in which the hob is masked over those portions which are to retain their original shape and size with the groove portions only exposed. The hob section is then inserted in an etching bath which will remove the metal on the exposed portions to a predetermined depth to form the grooves 48.

By adjusting the section i8 with respect to the section l4, the opposite side of the teeth on gear [2 from that engaged by the cutting edges 52 on the hob, is engaged by the smooth right angle side of the thread or section It. This will insure a proper intermeshing relationship between the hob I0 and the wheel l2. It is merely necessary then to run them in mesh so that the gear I2 is driven in a clockwise direction, in the embodiment illustrated, to shave one side of the teeth of gear l2. To shave the opposite side of the teeth, either the gear l2 may be turned upsidedown on its spindle or the hob It may be reversed end-for-end in its standard.

What is claimed is:

1. A globoidal cutting tool for cutting a worm gear of the Hindley type, said tool being formed of a pair 01' relatively movable sections, one of said sections having a portion of the thread of a worm formed thereon with a right angle side face and an angular side face extending from one end of the thread over said portion of the thread. portions of one of the side faces being provided with a plurality of spaced grooves extending at an angle to the radial from the root to the crest of the thread, said grooves having side walls intersecting said one of the side faces and being of materially less depth than the thickness of the thread, the edges of the grooves at the intersections between said face and side walls constituting cutting edges, the portions of the face forming lands between the cutting edges, said lands lying 2,348,844 in a common smooth surface, the other section having the remaining portion of the thread of the worm formed thereon, the faces of the remaining portion of the thread being smooth, and means to adjustably lock said sections with respect to each other.

2. A globoidaLcutting tool for cutting a worm gear of the Hindley type, said tool being formed of a pair of relativel movable sections, one of said sections having a portion of the thread of a worm formed thereon with a right angle side face and an angular side face extending from one end of the thread over said portion of the thread, said right angle side face being provided with a plurality of spaced grooves extending at an angle to the radial from the root to the crest of the thread, said grooves having side walls intersecting saidone of the side faces and being of materially less depth than the thickness of the thread, the edges of the grooves at the intersections between said face and side walls constituting cutting edges, the portions of the face forming lands-between .the cutting edges, and said lands lying inacommon smooth surface. said angular side face being smooth, the other section having the remaining portion of the thread of the worm formed thereon, both faces of the remaining portion of the thread being smooth, and means to adjustably lock said sections with respect to each other.

3. A globoidal cutting tool for cutting a worm gear of the Hindley type, said tool being formed of a pair of relatively movable sections, one of said sections having a portion of the thread of a worm formed thereon with a right angle side face and an angular side face extending from one end of the thread over said portion of the thread, said right angle side face being formed with a plurality of cutting edges extending at an angle to the radial from the root to the crest of the thread, said angular side face being smooth, the other section having the remaining portion of the thread of the worm formed thereon, both faces of the remaining portion of the thread being smooth and means to adjustably lock said sections with respect to each other. v

HARRY PELPHREY. 

